1. Field of the Invention
The present invention relates to networks, and more particularly to performing loop pathway integrity checks in a fibre channel arbitrated loop topology.
2. Background of the Invention
Fibre channel is a set of American National Standard Institute (ANSI) standards, which provide a serial transmission protocol for storage and network protocols such as HIPPI, SCSI, IP, ATM and others. Fibre channel provides an input/output interface to meet the requirements of both channel and network users.
Fibre channel supports three different topologies: point-to-point, arbitrated loop and fibre channel fabric. The point-to-point topology attaches two devices directly. The arbitrated loop topology attaches devices in a loop. The fibre channel fabric topology attaches host systems directly to a fabric, which are then connected to multiple devices. The fibre channel fabric topology allows several media types to be interconnected.
Fibre channel is a closed system that relies on multiple ports to exchange information on attributes and characteristics to determine if the ports can operate together. If the ports can work together, they define the criteria under which they communicate.
In fibre channel, a path is established between two nodes where the path's primary task is to transport data from one point to another at high speed with low latency, performing only simple error detection in hardware.
FC-AL is one fibre channel standard (incorporated herein by reference in its entirety) that establishes the protocols for an arbitrated loop topology. In a conventional FC-AL implementation there can be as many as 128 ports on the FC-AL loop. The data path consists of several transmit and receive paths.
During normal loop operation when Fibre Channel devices are connected, internal data path error, external data path error or interconnection error can cause a failure. Conventional systems do not have testing methods that isolate internal failure from an external failure or interconnection failure. A device causing a failure cannot be isolated using parity checking alone, other more robust testing methods like a CRC check are needed
Conventional fabric elements in a FC-AL topology are not robust and do not provide an efficient way to identify, isolate and manage loop traffic.
One such problem is shown in system 210 of FIG. 2B. System 210 includes a fibre channel element (or a switch) 216 that couples host systems 213-215 to storage systems 217 and 218. Storage system 217 and 218 include redundant array of independent disks (RAID) 211 coupled via plural input/output (“I/O”) modules and RAID controllers 201A and 201B. If drive 219 is defective, it may disrupt all traffic in common-access network 220. This can result in loop failure and lower performance of the overall network.
Another example is shown in FIG. 2A, where a RAID controller 201 is coupled to two different loops 209A and 208A via links 209 and 208 in a disk array system 200. Each loop has a small computer systems interface (SCSI) enclosure services (“SES”) module 202 and 202A. SES modules 202 and 202A comply with the SES industry standard that is incorporated herein by reference in its entirety.
Port bypass controller (“PBC”) modules 203 (and 206) couple plural disks (for example, 204, 202B and 207) and link 205 couples the PBC modules.
If drive 202B, which is dual ported, fails then both loops 209A and 208A are disrupted. Again, conventional techniques will require that storage 202A be removed and a bypass command issued to all drives, which takes the entire array off-line. Each device is attached and detached to investigate the reason for a link failure. Then all the drives, except the faulty drive are re-attached and loop activity is restored. This system of trial and error is labor intensive and inefficient.
Another drawback in conventional Fibre Channel networks is that loop functional test patterns and automatic test pattern generators (“ATPG”) are used to check individual L_PORTS. Conventional systems do not provide any tests that can check the entire FC-AL loop integrity. Also, there are no pattern generators that can generate an actual Fibre Channel frame with the correct encoding and disparity, consisting of a SOF, Header, Payload, correct Fibre Channel CRC, and EOF to check individual port integrity. Furthermore, de-bugging is performed on a trial and error basis when any failure occurs. Failures are debugged on a board one port at a time, which is tedious and time consuming and hence commercially undesirable.
Therefore, there is a need for a method and system for efficiently detecting FC-AL integrity.